The prices on some of the units are surprising. Battery operated fence chargers are nothing new to farmers and ranchers. You can get a 1.76 pound unit for $39 that will charge up to a MILE of fence and nearly 700 feet of tape-style wire for $18 (see http://www.horse.com/products/sku-BXW12.html for an example). All that you need from there are three trees or sticks, some antenna wire insulators from Radio Shack (or the feed store) and some light line to tie the insulators to the trees/sticks.